Research Updates: Should veterinarians emphasize the risk of intestinal nematodiasis based on patient signalment and geographic location?

Although intestinal parasitism in pet dogs is not uncommon, the relative distribution and frequency of the most common intestinal parasites (Toxocara, Ancylostoma, and Trichuris species) in various geographic regions of the United States have not been extensively studied. The authors’ goals in this study were, therefore, to determine the overall and regional prevalence of intestinal nematode parasitism in dogs and to identify signalment factors associated with increased risk of infection. Electronic medical records from about 1.2 million dogs examined between January 2003 and December 2006 at 547 Banfield-owned veterinary hospitals in 44 states were reviewed. Signalment and results of fecal nematode diagnostic tests were recorded; dogs were assigned to geographic regions previously defined by the Centers for Disease Control and Prevention (CDC) based on the owner’s home address. A total of 2,785,248 fecal flotation test results were obtained, with the prevalence for each parasite calculated as the number of positive dogs divided by the total number of dogs tested.

The prevalences of Toxocara, Ancylostoma, and Trichuris species infections in pet dogs in this study population were 5%, 4.5%, and 0.8%, respectively. Multiagent infections were uncommon, with only a single parasite genus recovered from most (82.7%) infected dogs. For all three parasites, intact dogs were more likely to be infected than neutered males or spayed females, and dogs in the west south central region (Arkansas, Louisiana, Oklahoma, and Texas) were more likely to be infected than those in other regions. Young (less than 0.5 years) and smaller (less than 5 kg) dogs had increased risk of Toxocara or Ancylostoma species infection and lower risk of Trichuris species infection. Conversely, dogs living in the mountain region (Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah, and Wyoming) and toy dogs had a significantly lower prevalence of intestinal parasitism compared with dogs living in all other regions or other AKC breed groups, respectively. Finally, despite an increase in the number of dogs tested per year over the study period, the prevalence of nematode infection decreased from 2004 to 2006.

COMMENTARYIntestinal nematodes in small animals are zoonotic, with possible major human health repercussions. As a result, treatment and prevention of infection in pets is a critical role of general veterinary practitioners throughout the world. The CDC recommends anthelmintic treatment for puppies at 2, 4, 6, and 8 weeks of age, and for kittens at 3, 5, 7, and 9 weeks of age. Unfortunately, veterinary compliance with methods of nematode detection is poor, and recommended deworming protocols and client education are inadequate throughout the world. For example, only 13% of surveyed Canadian veterinarians report strict compliance with CDC recommendations, only 31% of responding United States veterinarians recommended deworming puppies less than 4 weeks of age, and only 33% to 44% of American and Canadian veterinarians reported routinely discussing zoonotic risks of intestinal nematodes with their clients.1,2

The prevalences of the three intestinal nematode infections in pet dogs in the United States determined in this study are lower than in previous reports (5.7% to 15.5% for roundworms, 9.7% to 38.5% for hookworms, and 9.7% to 14.5% for whipworms).3,4 This decrease in prevalence of infection has been previously reported at Oklahoma State University, where the prevalences of confirmed Toxocara, Ancylostoma, or Trichuris species infections decreased from 8% to 4%, 39% to 15%, and 12% to 9%, respectively, between 1981 and 1990.5 This decrease in intestinal parasitism has been attributed to the increased availability of broad-spectrum anthelmintics and likely concomitant increased use as veterinarians’ awareness of the problem has grown.

This study reveals that important differences exist in the risk of intestinal nematode infection depending on signalment and geographic location. Although this information is important for general practitioners to help prioritize differentials in dogs with clinical signs of intestinal disease, whether this should influence routine deworming cannot be determined. For example, although a toy dog may be less likely to be infected with intestinal nematodes than dogs in other breed groups, the potentially closer relationship of toy breeds with their owners (higher percentage of time spent indoors or being held) may increase the risk of transmission. Because of the severity of the human diseases that may develop secondary to aberrant nematode migration and because deworming agents are cheap and their administration is without major side effects, it remains reasonable to continue routinely deworming all breeds, whatever the geographic location, following the recommended standard protocol.